The present application generally relates to controls for powertrains including regenerative start/stop alternator functionality (hereinafter referred to as “RSSA powertrain system(s)” or “RSSA powertrain(s)”), and more particularly but not exclusively to systems and methods of controlling RSSA powertrains including a supercapacitor. Various control strategies for RSSA powertrains have been attempted, but current proposals suffer from a number of limitations and drawbacks, including those respecting efficiency and integration of RSSA powertrain function with other systems and subsystems, among others. There remains a substantial need for the unique apparatuses, methods and systems disclosed herein.